As a pollutant to the environment, anionic detergents, after incorporated into a water body, accumulate on the surface of water and microparticles in the water, causing foaming or emulsification, which prevents oxygen from being incorporated into the water, and thereby leads to deterioration of water quality that jeopardizes organisms in the water.
According to the National Standard (GB17378.4—1998), the assay of anionic detergents in seawater is carried out by a spectrophotometric method using methylene blue, which is specified as follow: reacting an anionic-detergent-containing sample with methylene blue to yield a blue ion-pair compound, which is extracted into chloroform; measuring the absorbance of the extract at 650 nm, and expressing the assay result as the apparent concentration of sodium dodecylbenzene sulfonate. This method has the disadvantages of involving (1) time-consuming and complicated procedures due to the fact that each of the steps in the assay is carried out non-automatically, (2) the possibility of harming the working staff due to the toxicity of chloroform that is used as the solvent in the extraction step, and (3) a large consumption of chemicals.